The present invention relates to a piezoelectric/electrostrictive device comprising a movable portion to be operated by a displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting a displacement of a movable portion by a piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in the mechanical strength, impact resistance, and humidity resistance, and is capable of having the movable portion efficiently operated in large magnitude.
In recent years, in the fields of optics and magnetic recording, precision machining, and the like, a displacement element capable of adjusting an optical path length or position in sub-micron order has been required, and development has been progressed of a displacement element utilizing a displacement due to the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied on a piezoelectric/electrostrictive material (for example, a ferroelectric substance, or the like). For example, as shown in FIG. 20, a piezoelectric actuator 21, in which, by providing a hole 28 on a plate-like body composed of a piezoelectric/electrostrictive material, a fixing portion 25, a movable portion 24, and a beam 26 connecting therewith are integrally formed, and an electrode layer 22 is further provided on the beam 26, is disclosed in JP-A-10-136665.
In the actuator 21, when a voltage is applied across the electrode layer 22, the beam 26 expands or contracts in a direction in which the fixing portion 25 is connected with the movable portion 24 by the inverse piezoelectric effect or the electrostrictive effect, thus enabling the movable portion 24 to displace in an arc-shaped mode or a rotational mode in-plane of the plate-like body. On the other hand, JP-A-63-64640 discloses a technique with regard to an actuator utilizing a bimorph, wherein an electrode of the bimorph is split to be provided thereon, and the actuator is driven by selecting the split electrodes to perform precise positioning at a high speed, and for example, a structure in which two bimorphs are used mutually opposing is shown in FIG. 4 of the specification thereof.
However, with the actuator 21, as a displacement in the expansion/contraction direction (namely, in-plane direction of the plate-like body) of the piezoelectric/electrostrictive material is transmitted per se to the movable portion, there is a problem that an operational quantity of the movable portion 24 is small.
Further, the actuator 21, having all members thereof composed of a piezoelectric/electrostrictive material, which is fragile and relatively heavy in weight, has further problems, in addition to the mechanical strength being low, and being inferior in handling property, impact resistance, and humidity resistance, that the actuator 21 per se is heavy and is likely to be influenced by harmful vibrations (for example, residual vibrations or noise vibrations when operated at a high speed) in operation. In order to solve the above-described problems of the actuator 21, a proposition is made that the hole 28 is filled with a filler having flexibility, however, it is apparent that the efficiency of the displacement due to the inverse piezoelectric effect or the electrostrictive effect is decreased, when the filler is used.
On the other hand, what is shown in FIG. 4 of JP-A-63-64640 is that, in a bonding manner of a relaying member with a bimorph and a head with a bimorph, a so-called piezoelectric/electrostrictive operating portion expressing strain strides over each of the jointed portions, i.e., the bimorph strides continuously from the relaying member and the head. As a result, the displacement motion occurring from the jointed portion between the relaying member and the bimorph as a fulcrum and the displacement motion occurring from the jointed portion between the head and the bimorph as a fulcrum interfere with each other and hinder the development of the displacement when the bimorph is operated, and thus the structure is that an action for effectively displacing the head per se toward the outer space is unable to be obtained. In addition, the actuator disclosed in JP-A-63-64640 is so structured that a displacement generating member and a so-called frame member (intermediary member or the like) are separately prepared, and then adhered together to be incorporated, and consequently it is a structure where the joined state of the frame with the bimorph is likely to vary with time, and also drifting of a displacement, exfoliation, or the like is likely to be caused. Further, the structure having an adhesive intervened at the joined portion of a bimorph with an intermediary member and at the joined portion of a head with the bimorph, namely at a holding portion for a displacement member is also a structure where rigidity of the holding portion per se is low and it is difficult to obtain a higher resonant frequency which is required in high speed operation.
Although the present applicants have, of course, proposed a piezoelectric/electrostrictive device capable of solving such problems in the specification of the Japanese Patent Application No. 11-375581 and the like, development of a piezoelectric/electrostrictive device capable of obtaining still larger displacement quantity as well as capable of high speed response has been sought after as a precise positioning mechanism in the optical and magnetic recording fields.
The present invention is made in view of such current situation, and an object thereof is to provide a displacement element which is capable of increasing mechanical rigidity of joined portions of the thin plate portions with the movable portion and the thin plate portions with the fixing portion, facilitating higher resonant frequency, and further increasing displacement quantity of the movable portion, and a sensor element capable of efficiently detecting vibrations of the movable portion in higher precision.
According to the present invention, firstly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated by a drive of the driving portion, a fixing portion for holding the driving portion and the movable portion, the movable portion being coupled with the fixing portion via the driving portion, and a hole formed by inner walls of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion; in which the driving portion comprises a pair of mutually opposing thin plate portions and a piezoelectric/electrostrictive element including a piezoelectric/electrostrictive operating portion comprising a pair or more of electrodes and a piezoelectric/electrostrictive layer formed at least on a part of the outer surface of at least one thin plate portion of the pair of thin plate portions, one end of the piezoelectric/electrostrictive operating portion in a direction in which the fixing portion is connected with the movable portion exists on the fixing portion or the movable portion, the other end of the piezoelectric/electrostrictive operating portion is arranged on the thin plate portion, and at least the piezoelectric/electrostrictive layer of the piezoelectric/electrostrictive element exists extended over the movable portion and the fixing portion. Here, all of the movable portion, the thin plate portions, and the fixing portion may be comprised of either ceramics or metals, and additionally respective members may be comprised of different materials of metals or ceramics to give a hybrid structure.
Further, the present invention provides a piezoelectric/electrostrictive device in which the movable portion, the thin plate portions, and the fixing portion are integrally formed by simultaneously sintering a ceramic green sheet laminate, a piezoelectric/electrostrictive device in which the piezoelectric/electrostrictive element has a film-like piezoelectric/electrostrictive element directly formed on the thin plate portion and the movable portion or the fixing portion, and is integrally formed therewith by sintering, a piezoelectric/electrostrictive device in which a piezoelectric/electrostrictive layer constituting the film-like piezoelectric/electrostrictive element in which glass frit is not contained of, a piezoelectric/electrostrictive device in which the length L of the piezoelectric/electrostrictive operating portion disposed on the thin plate portion in the piezoelectric/electrostrictive element constituting the driving portion, together with the length e of the thin plate portion, satisfies the following expression, namely;
L=(50xc2x140)xc3x97e/100,
a piezoelectric/electrostrictive device in which the length L of the piezoelectric/electrostrictive operating portion disposed on the thin plate portion in the piezoelectric/electrostrictive element constituting the driving portion, together with the length e of the thin plate portion, satisfies the following expression, namely;
L=(50xc2x125)xc3x97e/100,
and a piezoelectric/electrostrictive device in which at least one piezoelectric/electrostrictive element out of piezoelectric/electrostrictive elements provided on the outer surface of a pair of mutually opposing thin plate portions has a multi-layered piezoelectric/electrostrictive operating portion.
Further, a piezoelectric/electrostrictive device of the present invention preferably comprises the movable portion, the thin plate portions, and the fixing portion, integrally formed in ceramics, more preferably comprises the movable portion, the thin plate portions, and the fixing portion composed of a material containing fully-stabilized zirconia as the major component, or a material containing partially-stabilized zirconia as the major component, and most preferably comprises at least the movable portion, the thin plate portions, and the fixing portion in a sintered ceramic green laminate. The reason is that joined portions with the movable portion, the thin plate portions, and the fixing portion can be structured to be without boundary by sintering integration, thus not only reliability at the portions can be raised, but also a phenomenon such as drifting or the like as variation with time of a device can be suppressed to be minimum, and a high displacement in a high speed can be developed with improved reproducibility. On the other hand, when composed of a metallic material as described previously, a device superior in handling property and impact resistance can be provided.
It should be noted, however, in fabricating a device according to the present invention, as to be described hereinafter, in addition to a device having all members thereof integrated by sintering, a device can also be obtained by a method wherein a laminate divided in a mutually opposing direction of the thin plate portion, namely a ceramic laminate comprising one thin plate portion and a member to be a fixing portion and a movable portion both in rectangular-solid shape is prepared, a piezoelectric/electrostrictive element is formed by the screen printing on a predetermined position as described previously for the thin plate portions, movable portion, and fixing portion of the ceramic laminate, at least two sintered structures integrally formed by sintering the piezoelectric/electrostrictive element with the above-described ceramic laminate are prepared, and the sintered structures are bonded together so as to have each of the thin plate portions mutually away, namely so as to have respective members to be a fixing portion and a movable portion mutually bonded by way of an adhesive or the like such as glass, an organic resin, or the like. However, the device fabricated first by having a movable portion, thin plate portions, and a fixing portion integrated by simultaneously sintering, then by forming a piezoelectric/electrostrictive element film on the sintered body, and then by having the body further sintered to be integrated, is superior in stability and reliability even if a stress is applied to the device by operation of the driving portion, as the device is not provided with a joined portion where the third party intervenes, or a so-called discontinuous portion of a structure, and this is preferable.
Further, a piezoelectric/electrostrictive device of the present invention preferably has a piezoelectric/electrostrictive layer, constituting a piezoelectric/electrostrictive element, composed of a material containing lead zirconate, lead titanate, and lead magnesium niobate as a mixture of the component, and a material containing sodium bismuth titanate as the major component is also preferable. Details of materials to be used are to be described later.
In the present specification, xe2x80x9cpiezoelectric/electrostrictive device (hereinafter simply referred to as xe2x80x9cdevicexe2x80x9d) is a notion implying an element for mutually converting electrical energy to mechanical energy via a piezoelectric/electrostrictive material. Accordingly, the piezoelectric/electrostrictive device is preferably used as an active element of a variety of actuators, vibrators, or the like, and specifically as a displacement element utilizing a displacement due to the inverse piezoelectric effect or the electrostrictive effect; and additionally a passive element of an acceleration sensor element, impact sensor element, or the like. Further, a piezoelectric/electrostrictive element means an element comprising a pair or more of electrodes and a piezoelectric/electrostrictive layer, being driven based on a signal to be transmitted, and performing a function for transmitting the movement thereof to a movable portion. In the element, a piezoelectric/electrostrictive operating portion means a portion for generating a predetermined strain according to a given signal, and substantially functioning in a piezoelectric/electrostrictive element, and comprises a portion where a pair or more of electrodes and a piezoelectric/electrostrictive layer are mutually superposed. Furthermore, to have a piezoelectric/electrostrictive operating portion in multi-layers means that a plurality of piezoelectric/electrostrictive operating portions are arranged in a layered mode in a direction perpendicular to the main surface of the thin plate portion, namely in the thickness direction of the thin plate portion. Further, respective electrodes constituting respective piezoelectric/electrostrictive operating portions may have a mode shared among operating portions, or a mode to be commonly used, or an independent mode. To the respective electrodes constituting respective operating portions, a predetermined signal is transmitted to activate an electric field on piezoelectric/electrostrictive layers constituting respective operating portions.
In the present invention, film-like means, to be described later, what is formed by a thick-film or a thin-film formation method, and ordinarily is differentiated from that formed by affixing a piezoelectric/electrostrictive element comprising a piezoelectric plate by an organic resin based adhesive. Further, xe2x80x9cpiezoelectricxe2x80x9d is meant herein by xe2x80x9cpiezoelectric and/or electrostrictivexe2x80x9d. Furthermore, xe2x80x9clengthxe2x80x9d means a distance in a direction in which the movable portion is connected with the fixing portion, namely in the Z-axis direction in the drawings, xe2x80x9cwidthxe2x80x9d means a distance in a direction penetrating through the hole, namely in the Y-axis direction in the drawings, and xe2x80x9cthicknessxe2x80x9d means a distance in laminating direction of a piezoelectric/electrostrictive element and the thin plate portion, namely in the X-axis direction in the drawings. It should be noted that those having the same or similar function in the drawings are marked, in principle, by the same symbol.